This study focused on the synthesis and evaluation of phosphine ligands with multiple
functional ities. Polar ligands suitable for use in homogeneous catalysis in aqueous/organic
systems were synthesised, as were ligands incorporating a boron atom in an intramolecular
Lewis acid-Lewis base interaction with the phosphorus atom.
A malonate moiety was readily incorporated into a phosphorus starting material, and
derivatives were obtained by reduction of the ester groups. The polar diol products were
reacted with 1,4-butanesultone which made them water soluble and thus ideal for biphasic
catalysis.
Wittig chemistry was employed to introduce alkenes of varying electronic nature into a
phosphorus-containing aldehyde starting material. The catalysed hydroboration reaction
making use of diboron reagents was used to introduce a boron functionality into the
resulting a, n-unsaturated ester phosphine I igands.
All of the ligands produced were tested in transition metal-catalysed reactions, namely the
Heck reaction, the Suzuki reaction, the Stille reaction, the carboxymethylation reaction and
the hydroformylation reaction. The polar and water soluble ligands all showed comparable
or improved yields to the standard benchmark triphenylphosphine ligand in organic,
biphasic and ionic liquid media. The electronic nature of the alkene ligands largely dictated the activities observed in the
Heck, Suzuki and Stille reactions. The electron rich ligands showed improved activities in
the Heck reaction, while the electron poor ligands showed improved activities in the Suzuki
reaction. In contrast, the Stille reaction seemed to be more affected by the steric demands
of the ligands rather than by electronic considerations. It was also found that the boron
containing ligands showed an enhanced activity in comparison to the boron free
unsaturated and saturated ester ligands. This enhancement was directly ascribable to the
Lewis acidic boron atom. This study allowed the synthesis of a range of functionally varying phosphine ligands
which where shown to influence transition metal-catalysed reactions based specifically on
the functionality present.